The laser frequency is stabilized to a resonance of the cavity using the Pound Drever Hall (PDH) frequency stabilization technique [1]}, [2]}. The required phase modulation at 2.5 MHz is created with an electro optic modulator (EOM). For frequency actuation the control loop uses a Piezo (PZT) actuator mounted to the NPRO crystal for fast frequency correction and the temperature of the NPRO crystal to stabilize long term frequency drifts. The control loop operates with unity gain frequencies up to 55 kHz.
